1. Field of the Invention
The present invention relates to a metering slide for fine-grained solids for gastight closing and cross-section-variable opening of vessels and piping in pneumatic conveying systems, whereby the sliding plate provided with a metering opening is moved by an appropriate drive means between two slide rings in a compression-proof slide casing.
2. Description of the Prior Art
Numerous fine-grained solids such as cement, metal powder, ceramic powder, artificial fertilizer, dust, e.g. the reflux of gas cleaning plant and flux for making slag for metallurgic methods, are pneumatically conveyed and metered. The fine-grained material is often located in silos from which it is withdrawn in different amounts and at varying flow rates.
Various possibilities of regulating such streams of material are known. It is possible, for example, to use a constant discharge cross-section on the storage vessel and to regulate the volume by means of varying pressure differences between the storage vessel and the space in which the fine-grained material flows. This volume regulation has disadvantages, however, with regard to the pressure differences to be adjusted in practice and the inertia this system involves to a certain degree. Special safety measures are also required when the inside pressure in the vessels increases.
It is also known to use metering valves on the storage bins of the powdery materials to control the amounts discharged, said metering valves working with a variable cross-section. This type of regulation works without any delays to a large extent and does not require any high pressure differences between the intake and discharge vessels. However, the metering openings are subject to higher wear, depending on the hardness of the material to be conveyed. Wear resisting materials such as hard metal and ceramics do not allow, on the other hand, for the discharge opening to be closed in a gastight manner, as proves to be necessary for most applications.
German Pat. No. 23 10 358 relates to an advantageous solution according to which a metering body and a sealing element are disposed, coupled with one another, one after the other in the direction of flow. The seal is effected in this case using known elastic sealing means when the cross-section is wider than the metering body. The disadvantages of this patented apparatus are the more elaborate construction and the larger space required.